Co-invasion of multiple invasive ants exacerbates the impacts on native ant communities

The structure and function of native ant communities are increasingly threatened by the growing number of biological invaders spread around the world. Although the detrimental impacts of single-species invasions on native ant communities have been well-documented, the ecological consequences of co-invasion events are poorly understood. We hypothesize that co-invasion impacts native ant communities more than single-species invasions. This effect is attributed to reduced discovery and recruitment times of invasive ants during co-invasion, ultimately bolstering their competitive advantage for food resources. We surveyed the taxonomic (TD), phylogenetic (PD), and functional (FD) diversity of native ant communities under varying levels of invasive ant presence and documented discovery and recruitment times of invasive and native ants at different baits. Results show that the taxonomic, functional, and phylogenetic diversity of native ant communities is significantly reduced in the presence of invasive ants compared to non-invaded communities. Moreover, the number of invasive ant species, or magnitude of co-invasion, exhibits a greater negative impact on native ant communities. Foraging competition assays demonstrate that the impacts of invasive ants are not immediately evident in metrics such as bait discovery and recruitment intensity, but are manifest in bait domination. The presence of invasive ants substantially reduced the proportion of bait occupied by native ants, and this effect intensified with more invasive species. In conclusion, co-invasion exacerbates impacts on native ant communities, with potential repercussions for broader ecosystems, warranting further attention.